In the officially bilingual Belgian capital Brussels, two independent education systems operate in parallel: a Dutch-language education system and a French-language education system. Pupils and parents can choose between both systems freely and independently of their home language background. Many Francophone parents prefer to enrol their children in Dutch-language schools in Brussels, because they believe this will stimulate their bilingual development. As a consequence of the massive inflow of French-speaking pupils in Dutch-language education in Brussels, an atypical form of education has emerged which we call "immersion-like education". In a previous cross-sectional study, the language skills of predominantly Dutch-speaking and predominantly French-speaking were tested. In this paper we will discuss the longitudinal development of Dutch L2 productive skills of native speakers of French across three consecutive school years. To assess their writing and speaking skills in their L2, predominantly French-speaking pupils were asked to write an informal letter to a friend, to write down arguments for and against a statement and to retell a wordless picture story. Based on these productions, three parameters were calculated: accuracy, complexity and fluency. In this paper, we describe the development of these parameters by means of repeated measures analyses of variance. We also discuss whether or not there is any relationship between these parameters. We ultimately address the question if this form of immersion-like education actually stimulates the development of bilingualism.